The bulls are bred specifically for the sport. If it were not for the sport, these bulls would not exist. Furthermore, the bulls have a very good life (they live the Life of Riley) before their admittedly frantic and cruel death.
I think bullfighting is cruel in one repsect, but in another it's an art form. I used to live in El Puerto de Santa Maria, Spain, which has the third largest bullring in the world. In fact, I lived on the same street as the bullring, so I witnessed at first hand the important role that bullfighting plays in the local culture. After watching bullfighting on TV and in the arena, I can appreciate the skill of the great toreros, and I also respect the people's right to practice this sport. Do I agree with it 100%? No. But then there are many things I don't fully agree with, however that doesn't mean they should all be banned.